The benefits of modifying fluoropolymers by vinyl ethers are described in various review articles. See, for example, Modern Fluoropolymers, John Scheirs, Wiley Series in Polymer Science 1997 and in other literature (e.g. Emel 'yanov et al, Zh. Org. Khim (1994) 30(8) 1266-70; Krespan, Carl G., DuPont de Nemours U.S. Pat. No. 4,273,728).
Partly fluorinated vinyl ethers and their copolymers are described in A. E. Feiring et al, DuPont de Nemours U.S. Pat. No. 5,326,917. Long chain vinyl ethers provide in fluoroelastomers excellent low temperature properties (see Uschold et al, U.S. Pat. No. 4,513,128).
The preparation of perfluoro(alkyl vinyl ethers) by fluorination with elemental fluorine is known. See Hung et al, U.S. Pat. No. 5,350,497. This patent discloses the fluorination of selected partially fluorinated (di)chloroethyl ethers (followed by dehalogenation to the corresponding perfluoro(alkyl vinyl ether).
Perfluorinated long chain perfluoroethers are difficult to prepare, especially those vinyl ethers without branching and more than 3 atoms in the alkyl group. For example, perfluorovinyl ethers are commonly prepared by two routes. See, for example, Modern Fluoropolymers, J. Scheirs, Wiley 1997 pp 376-378. ##STR1##
Addition of perfluorinated acid fluorides to hexafluoropropylene oxide results in an acid fluoride that may be converted to a salt and pyrolyzed to give the described perfluorovinyl ether. The oligomerization of hexafluoropropylene oxide with itself and conversion to a salt and subsequent pyrolysis gives long chain but branched ethers. ##STR2##
A more recent process prepares perfluorovinyl ethers by using perfluoro alkyl hypofluorites and dichlorodifluoroethylene followed by dehalogenation using, for example, Zn. ##STR3##
As noted, it is difficult to provide long chain perfluorinated ethers, especially vinyl ethers, when using these processes. A difficulty in the dichloro process includes the hazards of making and handling the R.sup.2.sub.f --OF species. Because of these hazards, this species also has a limited availability. An improved process for making perfluorinated vinyl ethers is needed, particularly for making linear perfluorinated vinyl ethers.